This invention relates to a process for concentrating gallium and, more particularly, relates to a process for concentrating and recovering gallium and recovering other valuable materials from dusts from the electric furnace production of phosphorus.
Gallium is found in association with zinc, germanium, aluminum and copper, and occurs in coals. Although the element gallium is relatively abundant, it is widely disseminated and, except in rare instances, the named sources often contain small concentrations only in the order of 0.001 to 0.02% gallium.
Many processes have been developed to concentrate gallium in the processing of ores of the above-named metals. For example, according to U.S. Pat. No. 1,855,455, which issued on Apr. 26, 1932, gallium is recovered from a zinc sulfide distillation reidue by treating the residue with hot, concentrated sulfuric acid, forming a solution containing gallium sulfate, treating the solution with hydrogen sulfide, electrolyzing the solution to deposit zinc, adding excess alkali and electrolyzing the solution to deposit gallium. According to U.S. Pat. No. 2,582,376, No. 2,582,377 and No. 2,582,378, which issued on Jan. 15, 1952, gallium is recovered from liquors from the Bayer aluminum process by insolubilizing some of the aluminum in the liquor as calcium aluminate, coprecipitating hydrated gallium oxide and alumina by introducing an acidic material such as carbon dioxide, dissolving the precipitate in alkali-metal hydroxide and electrolyzing the solution for deposition and recovery of gallium.
Gallium is also found in minuscule amounts in phosphate minerals and these amounts are somewhat concentrated during the processes for the production of elemental phosphorus. In these processes, for example, the gases leaving the electric furnaces are treated in precipitators for the collection of the flue dusts which contain gallium, as well as a large number of other elements, the most important of which are zinc, silver, cadmium, aluminum, phosphorous, sodium, potassium, calcium, fluorine, chlorine, silicon and carbon.
In U.S. Pat. application No. B 333,928, which was published on Jan. 28, 1975, there is disclosed a method of concentrating gallium from phosphorus-furnace treater-dust which comprises contacting the dust with an aqueous slurry of an alkaline-earth compound, separating the gallium-containing alkaline liquid from the dust and recovering the gallium from the liquid. The alkaline liquid may be carbonated to precipitate gallium, which may be recovered by known methods. The liquid may also be treated with hydrogen sulfide to form gallium-containing zinc sulfide, which may then be treated with acid and alkali to form a hydroxide precipitate from which the gallium may be recovered. This method has several disadvantages. The recovery of gallium is low. According to Example 1, 60% of the gallium in the dust remains in the residue and 60% (sic) of the gallium is extracted in the alkaline filtrate. According to Example 2, only 18.5% of the gallium in the dust is recovered in the final precipitate. No secondary or by-products appear to be recovered.
We have now found that phosphorus-furnace flue-dusts, named flue dust hereinbelow, can be treated for the concentration of gallium, for the economic recovery of gallium with high yields, and for the recovery of other values in the form of concentrates and solutions which can be further treated for the recovery of these values in valuable products.
Accordingly, it is an object of the present invention to provide a process for the recovery of values from flue dust.
It is another object to provide a process for treating flue dust for the separate recovery of metal values and fertilizer values.
It is a further object of the invention to provide a process for the concentration and recovery of gallium from flue dust.
These and other objects of the invention and the manner in which they can be attained will become apparent from the following detailed description of the process of the invention.